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Thalamic connectivity is crucial for the development of the neocortex. The pulvinar nuclei are thought to be particularly important for visual development due to their involvement in various functions that emerge early in infancy. The development of these connections constrains the role the pulvinar plays in infant visual processing and the maturation of associated cortical networks. However, the extent to which pulvino-cortical pathways found in adults are established at birth remains largely unknown, limiting our understanding of how these thalamic connections may support infant vision. To address this gap, we examined the organization of pulvino-cortical connections in human neonates using probabilistic tractography analyses on diffusion imaging data. Our findings revealed the presence of white matter pathways between the pulvinar and each individual visual area at birth. These pathways exhibited specificity in their connectivity within the pulvinar, reflecting both intraareal retinotopic organization and the hierarchical organization across ventral, lateral, and dorsal visual cortical pathways. These connections could enable detailed processing of information across sensory space and communication along distinct processing pathways. Comparative analyses revealed that the large-scale organization of pulvino-cortical connectivity in neonates mirrored that of adults. However, connectivity with ventral visual cortex was less adult-like than the other cortical pathways, aligning with prior findings of protracted development associated with the visual recognition pathway. These results deepen our understanding of the developmental trajectory of thalamocortical connections and provide a framework for how subcortical may support early perceptual abilities and scaffold the development of cortex.
Thalamic connectivity is crucial for the development of the neocortex. The pulvinar nuclei are thought to be particularly important for visual development due to their involvement in various functions that emerge early in infancy. The development of these connections constrains the role the pulvinar plays in infant visual processing and the maturation of associated cortical networks. However, the extent to which pulvino-cortical pathways found in adults are established at birth remains largely unknown, limiting our understanding of how these thalamic connections may support infant vision. To address this gap, we examined the organization of pulvino-cortical connections in human neonates using probabilistic tractography analyses on diffusion imaging data. Our findings revealed the presence of white matter pathways between the pulvinar and each individual visual area at birth. These pathways exhibited specificity in their connectivity within the pulvinar, reflecting both intraareal retinotopic organization and the hierarchical organization across ventral, lateral, and dorsal visual cortical pathways. These connections could enable detailed processing of information across sensory space and communication along distinct processing pathways. Comparative analyses revealed that the large-scale organization of pulvino-cortical connectivity in neonates mirrored that of adults. However, connectivity with ventral visual cortex was less adult-like than the other cortical pathways, aligning with prior findings of protracted development associated with the visual recognition pathway. These results deepen our understanding of the developmental trajectory of thalamocortical connections and provide a framework for how subcortical may support early perceptual abilities and scaffold the development of cortex.
The superior colliculus (SC) has been increasingly implicated in the rapid processing of evolutionarily relevant stimuli like faces, but the behavioural relevance of such processing is unclear. The SC has also been implicated in the generation of express visuomotor responses (EVR), which are very short‐latency (~80 ms) bursts of muscle activity time‐locked to visual target presentation. These observations led us to investigate the influence of faces on EVRs. We recorded upper limb muscle activity from healthy participants as they reached toward targets in the presence of a distractor. In some experiments, faces were used as stimuli. Across blocks of trials, we varied the instruction as to which stimulus served as the target or distractor. Doing so allowed us to assess the impact of instruction on muscle recruitment given identical visual stimuli. We found that responses were uniquely modulated in tasks involving high‐contrast faces, promoting reaches toward or away from a face depending on instruction. Follow‐up experiments confirmed that the phenomenon required highly salient repeated faces and was not observed to non‐facial stimuli nor to faces expressing different affects. This study extends the hypothesis that the SC mediates the EVR by demonstrating that faces impact muscle recruitment at short latencies that precede cortical activity for face perception. Our results constitute direct evidence for the behavioural relevance of face detection in the brainstem, and also implicate a role for top‐down cortical pre‐setting of the EVR depending on task context.
IntroductionIf neuroscientists were asked which brain area is responsible for object recognition in primates, most would probably answer infero-temporal (IT) cortex. While IT is likely responsible for fine discriminations, and it is accordingly dominated by foveal visual inputs, there is more to object recognition than fine discrimination. Importantly, foveation of an object of interest usually requires recognizing, with reasonable confidence, its presence in the periphery. Arguably, IT plays a secondary role in such peripheral recognition, and other visual areas might instead be more critical.MethodsTo investigate how signals carried by early visual processing areas (such as LGN and V1) could be used for object recognition in the periphery, we focused here on the task of distinguishing faces from non-faces. We tested how sensitive various models were to nuisance parameters, such as changes in scale and orientation of the image, and the type of image background.ResultsWe found that a model of V1 simple or complex cells could provide quite reliable information, resulting in performance better than 80% in realistic scenarios. An LGN model performed considerably worse.DiscussionBecause peripheral recognition is both crucial to enable fine recognition (by bringing an object of interest on the fovea), and probably sufficient to account for a considerable fraction of our daily recognition-guided behavior, we think that the current focus on area IT and foveal processing is too narrow. We propose that rather than a hierarchical system with IT-like properties as its primary aim, object recognition should be seen as a parallel process, with high-accuracy foveal modules operating in parallel with lower-accuracy and faster modules that can operate across the visual field.
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